readwritespinlock.cpp

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// The DAGFrameScheduler is a Multi-Threaded lock free and wait free scheduling library.
// © Copyright 2010 - 2014 BlackTopp Studios Inc.
/* This file is part of The DAGFrameScheduler.

    The DAGFrameScheduler is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    The DAGFrameScheduler is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with The DAGFrameScheduler.  If not, see <http://www.gnu.org/licenses/>.
*/
/* The original authors have included a copy of the license specified above in the
   'doc' folder. See 'gpl.txt'
*/
/* We welcome the use of the DAGFrameScheduler to anyone, including companies who wish to
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   However there are some practical restrictions, so if your project involves
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*/
#ifndef _readwritespinlock_cpp
#define _readwritespinlock_cpp

#include "atomicoperations.h"
#include "readwritespinlock.h"
#include "crossplatformincludes.h"
#include <limits>

/// @file
/// @brief Contains the implementation for the @ref Mezzanine::Threading::Mutex Mutex synchronization object.

namespace Mezzanine
{
    namespace Threading
    {
        ReadWriteSpinLock::ReadWriteSpinLock() : Locked(0)
        {}

        ReadWriteSpinLock::~ReadWriteSpinLock()
        {}


        void ReadWriteSpinLock::LockForRead()
        {}
        //{ while(!TryLockForRead()){} }

        bool ReadWriteSpinLock::TryLockForRead()
        {
            Int32 Expected = Locked;
            if(0<=Expected) // Can spuriously fail but shouldn't spuriosly succeed
            {
                return Expected==AtomicCompareAndSwap32(&Locked,Expected,Expected+1);
            }else{
                return false;
            }
        }

        void ReadWriteSpinLock::UnlockRead()
        {
            Int32 Expected = Locked;
            if(0>Expected)
                { return; }
            while(Expected!=AtomicCompareAndSwap32(&Locked,Expected,Expected-1))
                { Expected = Locked; }
        }

        void ReadWriteSpinLock::LockForWrite()
        {}
            //{ while(AtomicCompareAndSwap32(&Locked,0,1)) {} }

        bool ReadWriteSpinLock::TryLockForWrite()
            { return 0==AtomicCompareAndSwap32(&Locked,0,std::numeric_limits<Int32>::min()); }

        void ReadWriteSpinLock::UnlockWrite()
            { AtomicCompareAndSwap32(&Locked,std::numeric_limits<Int32>::min(),0); }



    } // \Threading namespace
} // \Mezzanine namespace
#endif